The present invention relates to a video disc and to a reproducing device therefor. More particularly, the invention relates to a video disc on which video and audio data signals are recorded in a multiplex mode and to a reproducing device therefor.
In general, both video data and audio data are recorded on a video disc. Two channels are provided for recording the audio data so that a stereo program or a "split" program (a program with two independent audio channels such as a bilingual program) can be recorded on the video disc. FIG. 1 shows a frequency spectrum of a data signal recorded on such a video disc. The two-channel audio signals and the video signal are converted into RF signals by frequency-modulating respective carrier signals before recording.
In general, the output of a video disc player (VDP) for reproducing data recorded on such a video disc includes, besides a baseband video signal and two-channel audio signals, a VHF signal generated, for example, according to the NTSC color television system. This signal is provided as a line output by the video disc player which can be connected directly to the VHF antenna terminals of a user's television set.
In the case where the audio signals are for a stereo program, a signal which is the sum of the two-channel signals or the difference between the two-channel signals is processed similarly as in the case of an ordinary stereophonic broadcast, and the relevant carrier signals are subjected to frequency modulation so that the signal thus processed and the video signal are converted into a signal in the VHF band which is outputted as a VHF signal.
In the case where the two audio signals are for a split program, the two independent audio signals are also processed similarly as in a television sound multiplex broadcast (currently in widespread use in Japan) and the carrier signals are subjected for frequency modulation so that the signals thus processed and the video signal are converted into a signal in the VHF band which is outputted as a VHF signal.
If the output VHF signal of the video disc player is connected to the VHF signal input of a home television set, then the sound multiplex program can be enjoyed if the television set is equipped with appropriate multiplex stereo receiving circuits. In this case, it is necessary to discriminate whether a sound multiplex program recorded on the video disc is a stereo program or a multiplex program and to process the output VHF signal output according to the discrimination result. In order to do so, or to obtain a desired VHF signal output, the user has to operate an audio channel change-over switch of the video disc player manually. Thus, the above-described system is disadvantageous in that the manual operation is troublesome and erroneous operations may be caused by the manual operation.